Plenty of disk space does not refer to the amount of actual hard drive memory. It's possible you may have an Anti-Virus which is trying to open and scan any file you open, which would mean Thunderbird gets blocked from access. I would recommend that you access the Anti-Virus and set up an exclusion to not scan your Thunderbird profile folders nor any of their contents. Then try again. Nor sure what OS you use nor whether you use an installation from the official Thunderbird download website or whether you got via Windows App Store or Snap or Flatpak etc. Is the gmail account an '''IMAP''' or '''POP''' account ? If Imap then gmail auto deletes anything that has been in that server folder after 30 days. Unless you have other settings. ''RE: I keep deleting old messages from the trash folder!'' Can you offer more info: Do you right click on the Trash folder and select 'Empty Trash' ? OR have you got this selected for the Account: In Account Settings > 'Server Settings' for the gmail account Under Message Storage Select 'Empty Deleted folder on Exit' I've been doing some checks on gmail Spam folder. It should have been empty. I did a compact, mbox file still with a load of emails, but I noticed the index file was more accurate. I did not get any errors about compacting. It just seemed to take a while with no X saved result. However, a repair folder had the desired result. please try this first: * Right click on folder and select 'Properties' * Click on 'REpair Folder' button * click on 'OK' Then check the profile folders gmail account folder to see if the size is more accurate.